PROJECT SUMMARY Peers play a powerful role in adolescents' adjustment. Deviant peer affiliation has consistently been linked to adverse outcomes among ethnic minority adolescents residing in urban communities, including substance use, aggression, and other delinquent behaviors. This is particularly concerning when taken with the disproportionate consequences that ethnic minority youth face for engaging in problem behaviors (e.g., school discipline). There is a critical gap in our knowledge of promotive factors that may reduce exposure to deviant peers and promote prosocial peer affiliation among ethnic minority adolescents across the middle school years, a period of heightened susceptibility to peer influence. The goal of the proposed study is to identify modifiable promotive factors that reduce the risk of problem behaviors by decreasing exposure to deviant peers and promoting prosocial peer affiliation. This focus aligns with NICHD's research priority of identifying mechanisms that promote psychosocial adjustment for youth exposed to high-risk neighborhood environments. The aims will be addressed through secondary analysis of a unique and rich data set with 12 waves of data that were collected every three months across all three grades of middle school (including the summers between each school year) between 2010 and 2018. Participants were a predominantly African American sample of 2,755 early adolescents living in urban communities with high rates of violence. Autoregressive models will be used to examine between- and within-person effects across each year of middle school. The specific aims are to: 1) examine the unique and combined influences of deviant and prosocial peer affiliation on problem behaviors within and across each grade of middle school, 2) determine the extent to which promotive factors (i.e., disclosure of activities to a caregiver, presence of a caring adult, positive future orientation) influence adolescents' peer group affiliation within and across each grade of middle school, and 3) investigate whether promotive factors reduce the risk of problem behaviors by decreasing exposure to deviant peers and promoting prosocial peer affiliation. Sex differences will be examined for each aim given that male and female adolescents have been found to differ in their susceptibility to deviant peer affiliation and problem behavior in previous work. Clarifying the complex relations among promotive factors for peer affiliation and problem behavior is essential to guide efforts to reduce risk and bolster positive development for youth living in urban communities with high rates of violence. The findings could inform these efforts by identifying change mechanisms and pinpointing times when interventions may be most effective within middle school. Further, the research and training outlined in this NRSA F31 pre-doctoral fellowship application will equip me with the skills and support needed to pursue a successful career as a research scientist, including knowledge of relevant theoretical models and their application to prevention efforts, competencies in advanced statistical methods for longitudinal research, and dissemination and grant-writing skills.